Techniques for manufacturing a bonding structure by bonding multiple bonded members with solder or bonding multiple bonded members with eutectic-bonding, with solder such as solder bumps or solder sheet or a eutectic-bonding insert metal interposed therebetween are widely used in semiconductor implementation steps. For example, in a semiconductor implementation step, a technique for bonding an organic substrate and a semiconductor substrate with solder with solder bumps interposed therebetween and a technique for bonding a semiconductor substrate and a semiconductor chip with solder with solder bumps interposed therebetween are employed.
For example, when semiconductor substrates (semiconductor chips) are bonded with solder, it is necessary to remove an oxide film on the surface of the solder bump in order to melt the solder bump and bond multiple substrates with solder. In order to do this, multiple substrates are stacked and heated while a rosin-based reducing organic agent, which is called “flux”, is applied to the surface of the substrate. As a result, preferable solder bonding is made while the oxide film on the surface of the solder bump is reduced and removed by the flux. After the solder bonding is made, the flux is removed by cleaning treatment such as solution cleaning and ion etching.
However, in recent years, the decrease in the size of the solder bump structure makes it difficult to remove the flux. In particular, when the pitch interval between adjacent solder bumps or the diameter of the solder bump becomes several dozens of μm or less, it is difficult to sufficiently remove the flux. The flux that could not be removed makes flux residue. Due to the effect of chlorine included in the flux, the flux residue may cause insulation failure, which is called migration, between adjacent electrode structures (solder bumps). In a step of finally filling an underfill resin between substrates, the flux residue makes it impossible to sufficiently fill the underfill resin, which makes clearance that is called void.
On the other hand, a method for omitting cleaning treatment using flux-less solder bonding (cleaning-less method) is actually used as a method for eliminating the effect of the flux residue. More specifically, carboxylic acid vapor such as formic acid is introduced into a chamber, and the oxide film on the surface of the solder bump is reduced by this carboxylic acid, so that this makes it possible to make solder bonding without using any flux (Cited documents 1, 2).
However, flux-less solder bonding raises a new problem in that it is likely to cause positional displacement between substrates. More specifically, as described above, when the flux is used, retaining force (stack force) occurs due to the flux residing between the multiple substrates, and this retaining force prevents the positional displacement of the substrates from one another. In contrast, with the flux-less solder bonding, there is no flux between the substrates, and the retaining force (stack force) cannot be given between the substrates. For this reason, in the cleaning-less method based on the flux-less solder bonding, it is likely to cause positional displacement between substrates, and this imposes limitation on cases where the cleaning-less method can be applied. In particular, when the substrates are bonded with solder with the solder bumps on the substrates, a positioning accuracy may be required to be about 1 to 2 μm, and therefore, it is difficult to apply the cleaning-less method, which is likely to cause positional displacement. Similar problems may occur with eutectic-bonding.
Further, the positional displacement causes the problem not only when the substrates are bonded but also when a solder material is fixed onto a substrate and solder bumps are formed, for example.